This invention relates generally to testing of circuit boards, and more particularly to improvements in test fixtures used for such purposes.
Such fixtures presently include upper and lower insulative plates, the circuit board removably supported on the upper plate to present its solder connections for engagement with test probes associated with the lower plate. Vacuum applied to the space between the plates effects relative movement of the upper plate and circuit board toward the lower plate, to engage the test probes with the solder or printed connections, leads, etc. at the underside of the circuit board.
One problem that exists is the tendency for the test probes to exert sufficient force on the circuit board as to break the seal between that board and the upper plate, whereby the vacuum urging the top plate toward the lower plate is destroyed, and testing is interrupted. The problem increases as the number of test probes needed to test the circuitry on the board increases, and since the total force tending to lift the circuit board and break the vacuum increases as a function of the number of spring urged test probes utilized.
Another problem that arises is the difficulty of removing the upper plate off the test fixture for maintenance purposes--i.e. to allow clean-out of solder particles from the space between the boards, such particles otherwise increasing the risk of electrical shorts, as by engagement with test probes. Presently, the structures used to limit upper plate downward displacement toward the lower plate during testing, project through the upper plate, and it requires release of all such multiple structures before the upper plate can be lifted away, to expose the space between the plates.